1. Field of the Invention
The present invention relates to a photoelectric conversion element composed of silicon non-single crystalline material, a fabrication method thereof, and a power generation system using the photoelectric conversion element.
Particularly, the invention relates to a photoelectric conversion element wherein the bandgap of a pin-type photoelectric conversion semiconductor is changed, and a deposition method of said photoelectric conversion element by plasma CVD.
2. Related Background Art
In the prior art, various proposals have been made for a photoelectric conversion element of the pin-type structure composed of silicon non-single crystalline material, in which an i-type layer contains silicon and germanium atoms, with the bandgap varying in the i-type layer. For example, the following have been reported:
(1) "Optimum deposition conditions for a-(Si, Ge):H using a triode-configured rf glow discharge system," J. A. Bragagnolo, P. Littlefield, A. Mastrovito, and G. Storti, Conf. Rec. 19th IEEE Photovoltaic Specialists Conference, 1987, pp. 878-883. PA1 (2) "Efficiency improvement in amorphous-SiGe:H solar cells and its application to tandem type solar cells;" S. Yoshida, S. Yamanaka, M. Konagai, and K. Takahashi, Conf. Rec. 19th IEEE Photovoltaic Specialists Conference, 1987, pp. 1101-1106. PA1 (3) "Stability and terrestrial application of a-Si tandem type solar cells," A. Hiroe, H. Yamagishi, H. Nishio, M. Kondo, and Y. Tawada, Conf. Rec. 19th IEEE Photovoltaic Specialists Conference, 1987, pp. 1111-1116. PA1 (4) "Preparation of high quality a-SiGe:H films and its application to the high efficiency triple-junction amorphous solar cells," K. Sato, K. Kawabata, S. Terazono, H. Sasaki, M. Deguchi, T. Itagaki, H. Morikawa, M. Aiga, and K. Fujikawa, Conf. Rec. 20th IEEE Photovoltaic Specialists Conference, 1988, pp. 73-78. PA1 (5) U.S. Pat. No. 4,816,082 PA1 (6) U.S. Pat. No. 4,471,155 PA1 (7) U.S. Pat. No. 4,782,376 PA1 (8) "A novel design for amorphous silicon alloy solar cells," S. Guha, J. Yang, A. Pawlikiewicz, T. Glatfelter, R. Ross, and S. R. Ovshinsky, Conf. Rec. 20th IEEE Photovoltaic Specialists Conference, 1988, pp. 79-84. PA1 (9) "Numerical modeling of multijunction, amorphous silicon based P-I-N solar cells," A. H. Pawlikiewicz and S. Guha, Conf. Rec. 20th IEEE Photovoltaic Specialists Conference, 1988, pp. 251-255.
Also, several theoretical researches on the characteristics of a photovoltaic element having a variable bandgap have been reported, for example,
Such photovoltaic elements in the prior arts have a varying bandgap layer inserted into p/i and n/i interfaces for preventing recombination of photoexcited carriers in the vicinity of the interfaces, increasing open-circuit voltage, and enhancing carrier range of holes.